Mast cells are a unique hematopoietic cell that is resident only in tissue and not in the blood stream. They are sentinels, constantly on the lookout for invading organisms, toxic molecules and tissue damage. When mast cells encounter such pathogens or damage, they release a flood of mediators; these mediators are a mix of small molecule effectors (such as histamine), proteases, lipid-derived signaling molecules (prostaglandins) and cytokines. The process of releasing these mediators is generically termed “degranulation.”
The release of mediators via degranulation results in the recruitment of a wide variety of immune cells to the site of mediator release to fight the offending intruder. This process also induces localized inflammation to restrict the movement of any infection or toxin. A controlled inflammatory response to foreign bodies enables the body to prevent the spread of toxins to neighboring tissues, limiting damage to one area and is desirable. Once the toxin has been neutralized, the normal course is for the body to begin an active resolution of inflammation response (ROI). This results in an egress of recruited immune cells from the injured tissue, tissue remodeling, a reduction in swelling and finally complete healing.
In some cases, this normal course of a proportional inflammatory response, followed by resolution is not followed. This can result in either a chronic state of inflammation or an overly robust mediator response that is out of proportion to the invading event. The latter scenario has been termed a “cytokine storm” or hypercytokinemia. An extremely high level of inflammatory cytokines and mediators that is not resolved is harmful to the host and can result in death, especially if the run-away response occurs in the lungs. The most damaging aspects and symptoms of many diseases are a direct result of hypercytokinemia, as opposed to damage from the original disease.
Current treatments for conditions that induce hypercytokinemia do not generally do anything to ameliorate the ongoing production of inflammatory mediators that perpetuate this condition. These conditions are usually treated by interventions that target the pathogen inducing the response or by using antagonists to one specific inflammatory mediator. While it is critical for the pathogens to be neutralized, in most diseases that induce hypercytokinemia, the problem is not the pathogen, but rather the body's overly robust response to the pathogen by a dozen or more inflammatory mediators.
Nevertheless, down regulating the immune system is not enough on its own to treat these conditions. In fact, there is evidence in some cases suggesting that treating patients with corticosteroids to reduce inflammation increases mortality. Corticosteroids are very powerful down regulators of the innate and adaptive immune system. “Turning off” all aspects of the immune response during an infection does not allow the clearance of the pathogen. Thus, a balance must be struck between an overly robust immune response and too little of a response.
Influenza viruses are a related series of viruses in the Orthomyxoviridae family. Three types have been described (Types A, B or C) and all are negative-sense, segmented, single stranded RNA viruses. Types A and B are medically relevant to human health with type A being the cause of more severe disease. Type A viruses are normally found in wild birds and only rarely cause disease in their host. Influenza A subtypes routinely cause waves of human influenza disease across the globe with far reaching health and economic consequences. In the US, approximately 30,000 people die each year from flu or complications resulting from influenza infection. The estimates on economic impact in the US are greater than $80 billion/year in direct medical costs and lost work. Influenza usually infects humans through the respiratory tract, although there are also reports that infection can occur through the eyes.
Influenza induces a rapid cytokine response in humans, usually detectable within hours of infection. An important point to note is that the severity of each case of flu is directly correlated with the levels of induced cytokines. This is well known to those in the field and has been documented across many different strains of influenza. What is particularly striking about influenza induced disease is that severity is dependent on the viral strain and the individual. For instance, most yearly cases of influenza are caused by the H1N1 strain. While many people are infected, the severity of the disease ranges from no symptoms to death. In a normal H1N1 seasonal flu season in the US, about 20% of the population are sickened (60 million people), 200,000 of those are hospitalized and about 30,000 people die each year (about 0.05% mortality). In outbreaks involving highly pathogenic strains of the virus (H5N1 for instance) 30% to 60% of the cases are fatal. While this indicates that the virus is the main cause of severity, the reason that people exhibit more severe or fatal disease is the same with either strain: the dangerously ill people have extremely high levels of cytokines, regardless of viral strain. Thus, the problem is not really the virus itself, but rather the body's response to the virus. In more virulent strains, a larger proportion of people will experience hypercytokinemia. However, this hypercytokinemia is no different than it is in the small proportion of people that experience the same symptoms from a less virulent strain.
Mast cell stabilizers such as ketotifen and cromolyn (sodium cromoglycate) have been shown to inhibit mast cell degranulation and the resulting release of mediators such as histamine, tumor necrosis factor (TNF)-α, prostaglandins, leukotrienes, interleukins and other cytokines. These effects may not be limited to mast cells and might have a broader effect of reducing inflammatory cytokine release in multiple cell types. These compounds, however, do not impact the adaptive immune system and allow antibody based clearance of foreign bodies from the body to continue essentially as normal. Both of these compounds are used to treat chronic conditions. Cromolyn was discovered and used as an inhaled treatment for asthma. Ketotifen was discovered as an H1 antihistamine and is used extensively in eye drop formulations to treat eye inflammation. It was also developed as an oral treatment for asthma, although this seems to take several weeks for it to have significant impact on chronic asthma. Ketotifen and to a lesser extent cromolyn have been shown to increase survival of mice in a model system of influenza infection (Hu et al., Mast Cell-Induced Lung Injury in Mice Infected with H5N1 Influenza Virus, J. Virol. 86(6):3347 (2012); Han et al., The therapeutic effects of sodium cromoglycate against influenza A virus H5N1 in mice, Influenza and Other Respiratory Viruses 10(1):57 (2016)). In the case of ketotifen, it was combined with oseltamivir and the impact on survival was increased when the compounds were combined.
The present invention overcomes shortcomings in the art by providing compositions and methods for treating hypercytokinemia and disorders associated therewith.